The present invention relates to a method for controlling internal pressure in a mold cavity in a moving-mold type continuous casting machine for continuously permitting molten metal to be cast into a casting.
In general, in a moving-mold type continuous casting machine, a plurality of block molds a are interconnected with each other in the form of an endless track to thereby provide a mold assembly b as shown in FIG. 1. Such two mold assemblies b are disposed one upon another in spaced apart relationship to define a mold cavity c. A tundish nozzle d is inserted through one opening of the mold cavity c so as to pour molten metal e in the mold cavity c. The mold assemblies b and a solidified casting f are continuously moved toward the other opening of the mold cavity c. In this manner, the continuous casting is carried out.
If molten metal penetrates into a gap defined between a portion of the tundish nozzle d inserted in the mold cavity c and the mold assembly b and solidifies, not only the tundish nozzle d but also the casting f are damaged. Therefore, the gap is to be reduced for prevention of the molten metal from penetrating thereinto.
However, when the above-mentioned gap is extremely reduced, the gap becomes disappearable due to vibrations produced during the movement of the mold assemblies b which are very heavy in weight so that the tundish nozzle d contacts the mold assemblies b and is readily damaged.
Thus, the above-mentioned gap cannot be made too narrow. It is almost impossible in the present state of art to maintain the gap less than 0.15 mm, without the possibility of disappearance due to vibrations, because of limited dimensional accuracies of various mechanical component parts including the tundish nozzle.
It follows therefore that since the gap is practically 0.15 mm at the least, a vertical height between the leading end of the tundish nozzle d and the surface level of molten metal e within a tundish g, i.e., a molten metal static pressure height H is to be lowered to some extent; but in general the height of the surface level of molten metal e in the tundish g is as high as 0.5 m or more.
Furthermore, conventionally the tundish nozzle d is disposed in an inclined position for facilitation of widthdrawing of the casting f out of the mold cavity c so that the tundish nozzle d is increased in length correspondingly and the molten metal static pressure height H is further raised.
As a result, conventionally, it is almost impossible to avoid molten metal from penetrating into the gap.
The inventors made extensive studies and experiments to overcome the above problems and found out that the gap .delta. (in mm) and molten metal static pressure height H (in m) which allow the molten metal to penetrate into the gap due to surface tension have the relationship as shown in FIG. 2.
As is clear from FIG. 2, when the gap is 0.15 mm or more and if the molten metal static pressure height H is 0.3 m or less, no molten metal is allowed to penetrate into the gap.
Thus, the present invention was made based on the fact that the penetration of the molten metal into the gap can be prevented by controlling a molten metal static pressure in the mold cavity c to a level corresponding to molten metal static pressure height H of 0.3 m or less.
Therefore in a moving-mold type continuous casting machine of the type in which a pair of endless-track type block mold assemblies each wrapped on a pair of spaced sprokets are disposed one upon another and spaced apart from each other so that opposing surfaces of the mold assemblies are moved in same direction to define a mold cavity; and molten metal is poured into the mold cavity through a tundish nozzle inserted in the mold cavity, whereby the molten metal is allowed to cool and solidify in the mold cavity into a casting, the present invention provides a method for controlling the internal pressure in the mold cavity of the moving-mold type continuous casting machine of the type described above, comprising the steps of detecting a molten metal static pressure within the mold cavity and then controlling a quantity of molten metal poured into the mold cavity through the tundish nozzle such that the molten metal static pressure within the mold cavity can be maintained at a predetermined level.
Regardless of the height of the surface level of molten metal in the tundish, the quantity of molten metal poured through the tundish nozzle is controlled by, for instance, variable throttling means so that the molten metal static pressure in the mold cavity is always maintained at the predetermined level and the quantity of the molten metal penetrating into the gap between the tundish nozzle inserted in the mold cavity and the opposing surfaces of the endless track type mold assemblies can be reduced to a minimum.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of a preferred embodiement thereof taken in conjunction with the accompanying drawings.